Population modeling system based on multiple data sources having missing entries

ABSTRACT

A neural network is used to model to model the joint distribution of attributes across multiple health surveys. These multiple health surveys include large scale survey datasets and small scale survey datasets. The neural network model is trained using a combined dataset of the large scale survey datasets and the small scale survey datasets. The large scale survey datasets and the small scale survey datasets may include missing value indicators. The joint distribution of attributes modeled by the neural network model are the used to impute substitute values for the missing values to thereby create an output large scale dataset that does not include missing values.

FIELD OF THE INVENTION

Embodiments relate generally to the combining of data from multiplesources with missing values and modeling a population based on thosemultiple sources.

TECHNICAL BACKGROUND

A recurring challenge that public health agencies face is determininghow best to achieve certain outcomes for their constituents—such asbetter health. One approach to guide policy decisions is populationmodeling. Population modeling can help give a better understanding andcharacterization of a target population and how their behaviors maychange in response to various policies that could be implemented withthe purpose to improve population health. Population modeling can alsohelp with understanding the impact of policies, interventions,incentives on the population and the effect of those policies,interventions, incentives on outcomes of interest (e.g., heart diseaserates) given that the population is diverse.

OVERVIEW

In an embodiment, a method includes training a first neural networkmodel to model the joint distribution of attributes across multiplehealth surveys. These multiple health surveys include large scale surveydatasets and small scale survey datasets. The first neural network modelis trained using a combined dataset of the large scale survey datasetsand the small scale survey datasets. The large scale survey datasets andthe small scale survey datasets may include missing values. The jointdistribution of attributes modeled by the neural network model are usedto impute the missing values to thereby create an output combineddataset that does not include missing values.

In an embodiment, a method includes receiving heterogenous survey datacomprising at least a first dataset having a first set of attributes anda second dataset having a second set of attributes. The first set ofattributes and the second set of attributes have at least one commonattribute, and at least one attribute that is not in common between thefirst set of attributes and the second set of attributes. The firstdataset and the second dataset also having at least one missing entry.The method further includes training a Restricted Boltzmann Machine(RBM) having hidden nodes and visible nodes using the first dataset andthe second dataset. The training includes, for a missing entry in atleast one of the first dataset and the second dataset, estimating avalue for the missing entry based on a first randomly selected samplemade according to a first joint probability distribution of a value forthe missing entry given a set of current visible node values and a setof current values for the hidden nodes.

In an embodiment, a system includes a first neural network modelconfigured to model the joint distribution of attributes across multiplehealth surveys. The multiple health surveys include large scale surveydatasets and small scale survey datasets. The first neural network modelis trained using a combined dataset of the large scale survey datasetsand the small scale survey dataset. The large scale survey datasets andthe small scale survey dataset include missing values. The system alsoincludes an imputation module to use the joint distribution ofattributes modeled by the first neural network model to imputesubstitute values for the missing values to thereby create an outputlarge scale dataset that does not include missing value.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an example population modelingsystem.

FIG. 2 is a flowchart illustrating a method of data preprocessing.

FIG. 3 is a flowchart illustrating a method of batch-wise training aneural network model.

FIG. 4 is a flowchart illustrating a method of imputing values formissing data.

FIG. 5 illustrates a processing node.

DETAILED DESCRIPTION

In an embodiment, a neural network model to model the joint distributionof attributes across multiple health surveys. These multiple healthsurveys include large scale survey datasets and small scale surveydatasets. The neural network model is trained using a combined datasetof the large scale survey datasets and the small scale survey datasets.The large scale survey datasets and the small scale survey datasets mayinclude missing values. In other words, the survey dataset may havemissing values that may result from, for example, different questionsbeing part of the large scale survey dataset and the small scale surveydataset or non-responses by participants in the surveys. The jointdistribution of attributes modeled by the neural network model are theused to impute values for the missing values to thereby create an outputlarge scale dataset that does not include missing values.

FIG. 1 is a block diagram illustrating an example population modelingsystem. In FIG. 1, system 100 comprises large scale survey data 151,small scale survey data 152, data preprocessing 161, data preprocessing162, feature realignment 171, data fusion module 131, datatranslation/model building module 111, microsimulation module 181,application/dashboard module 182, and augmented survey data 153.

In FIG. 1, large scale survey data 151 is provided to data preprocessing161. The output of data preprocessing 161 is provided to featurerealignment 171. The output of feature realignment 171 is provided todata fusion module 131. Outputs of data fusion module 131 are providedto data translation/model building module 111, microsimulation module181, and application/dashboard module 182. Outputs of datatranslation/model building module 111 are provided to microsimulationmodule 181, application/dashboard module 182. Data translation/modelbuilding module 111 also produces augment survey data 153. Augmentedsurvey data 153 is provided to application/dashboard module 182.

Large scale survey data 151 is, for example, data produced by one ormore surveys that are done at a national level. These surveys aretypically done by, or at the behest of, Government agencies. Large scalesurvey data 151 is based on a survey where a very large samplepopulation is questioned. One example of large scale survey data 151 isBehavioral Risk Factor Surveillance System (BRFSS). For BRFSS, around500,000 people throughout the United States are surveyed each year.Questions asked in such large scale surveys are typically easilyanswerable and people usually have good and near accurate knowledge ofthe answers (e.g., Weight, Height, Age, etc.). The sample populationbeing questioned may be very carefully designed through a method calledstratified sampling such that it can be used to obtain distributions atnational level, state level or county level.

Small scale survey data 152 is, for example, data produced by one ormore surveys are designed by either government agencies or otherprivate/public institutes to obtain data on particular attributes of thepopulation. Typically, these attributes are such that their measurementis either not straightforward from an implementation or an economicpoint of view. This tends to limit the sampled population size of thesesurveys. Because of the limitation in sampled population size, it maynot be a stratified sample where these surveys are representative ofindividuals, families and population subgroups at zip code and countylevel at the same time. Trying to capture the statistics of theseattributes at every zip code level would make these surveys veryexpensive. Examples of such expensive to survey attributes arebiomarkers such as Blood sugar levels and cholesterol levels—whichrequire for measurement laboratory testing. One example of a small scalesurvey 152 is National Health and Nutrition Examination Survey (NHANES).NHANES surveys about 5,000 people each year which is around 10% of thenumber of people surveyed by the large scale survey data 151 BRFSS. Inother words, in an embodiment, large scale survey data 151 will include10× more people in the survey than small scale survey 152.

Feature realignment 171 processes the input data from multiple sources(e.g., large scale survey data 151 and small scale survey data 152) suchthat the responses are in a common space. Because different surveys havedifferent objectives and hence different attributes of interest, not allattributes are measured/quantified with the same granularity within andacross these multiple surveys. For example, a survey whose objective isto understand smoking habits will have detailed (and more) questionsregarding smoking such as the number of cigarettes smoked daily andresponses to which will be quantified into greater number of resolutionlevels. Whereas a more generic survey may have the smoking informationin form of just a “yes/no” reply. The feature realignment module willbin the categories of the more granular survey question so that thegranularity of the more granular survey question matches the granularityof the less granular survey question.

Data fusion module 131 includes a neural network that is trained tomodel the joint distribution of all the attributes across these multiplesurveys. In operation, once the preprocessing of large scale survey data151 and small scale survey data 152 by data preprocessing 161, datapreprocessing 162, and feature realignment 171 is complete, all thesurvey data is merged together to create a combined dataset. When thesame question is asked in the small scale dataset and the large scaledataset, there may be missing values denoting survey non-response. Whena question is asked in the small scale survey dataset but not in thelarge scale survey dataset, there will be missing values for eachsurveyed person in the large scale surveyed dataset and for somesurveyed people in the small scaled dataset who don't respond. When aquestion is asked in the large scale survey dataset but not in the smallscale survey dataset, there will be missing values for each surveyedperson in the small scale dataset and some surveyed people in the largescale dataset who don't respond.

For each row of the combined dataset where there are missing values, itis possible to substitute any response of the survey question for itsvalue. However, some responses are expected to be more likely than otherresponses based on other values in any particular row. Data fusionmodule 131 operates to fit a parametric joint distribution thatmaximizes the likelihood of each missing survey response question in thecombined dataset. In an embodiment, Data fusion module 131 is based on asingle Restricted Boltzmann Machine (RBM) that is trained using all thesurvey datasets. The single RBM can be trained using rows with anynumber of missing entries.

Data translation/model building module 111 uses the joint distributionlearned in the DataFusion Module, to impute the missing value entries,the attributes from the smaller focused surveys that were not asked inthe large scale survey and the attributes from the large scale surveydata that were not asked in the small scale survey. Output of thismodule can then serve as a basis to create machine learning models thatestimate unknown attributes of a population from known attributes of apopulation. Known attributes of a population that may exist at thegranularity of a zip code, county, state and the whole nation mayinclude demographics such as age, gender, and ethnicity as well associoeconomic status such as income and education. Unknown attributes ofa population may include unhealthy behaviors (like smoking, alcoholintake etc.), biomarkers (like BMI and blood HbA1C level), and healthstates (like diabetes or heart disease).

Microsimulation module 181 uses the machine learning models which arethe output of data fusion module 131 to simulate the attributes of anentire population representative of an area at the granularity of a zipcode, a county, a state, or the nation as a whole. The attributes mayinclude the demographics, the socioeconomic status, unhealthy behaviors,biomarkers, and health states. The excess medical burden associated withthe population health states can also be calculated. The simulationpopulation can be progressed in time based on these models to extracthow unhealthy behaviors, biomarkers, and health states of the populationchange over time. The models may include the how unhealthy behaviors andbiomarkers and thus health states may respond to various interventionsand policies. Multiple simulations can be run over multiple zip codes,counties, and states to model the effective of various interventions andtheir associated costs over different geographical areas.

The result of running the multiple microsimulation models is thedemographics, unhealthy behaviors, biomarkers, health states, and excessmedical burden of a population and how these attributes changed overtime. These attributes can be presented to an analyst with theapplication/dashboard module 182. The analyst can use theapplication/dashboard module to explore projected health care costs overvarious geographic areas and determine the best use of finiteintervention resources. The application/dashboard module 182 also actsas a front-end for the analyst to run the microsimulation module 181.

FIG. 2 is a flowchart illustrating a method of data preprocessing. Thecombining of multiple surveys begins with loading a first dataset #1(201). The first dataset may contain only a subset of the informationthat is required to completely characterize an individual. For example,the first dataset may contain demographic, socioeconomic, behavior, andhealth information about individual respondents, but not labs tests suchas A1C or cholesterol level. The first dataset typically contains onerow for each individual surveyed. The first dataset may contain numericattributes such as age or weight which can take any value on acontinuum. The dataset may also contain categorical attributes such asrace which take on a finite number of values. The individuals surveyedmay not answer one or more questions so each row of the dataset maycontain one or more missing values. This first dataset may be, forexample, a phone survey where it is easy to reach many respondents andcan be considered large survey dataset (e.g., large scale survey data151.)

Numeric attributes are binned (202). For example, the RestrictedBoltzmann Machine (RBM) algorithm requires all attributes to becategorical attributes and not numeric attributes. Therefore, thenumeric attributes in the first dataset are binned into a finite numberof categories—thus converting the numeric attributes to categoricalattributes. For example, ages of adult respondents which vary between 18and 100 can be binned into categories of young between 18 and 40, middleaged between 40 and 60, and old between 60 and 100.

Dataset #2 is loaded (203). The second dataset may, for example, containa different subset of the information that is required to completelycharacterize an individual. The second dataset may, in addition to thedemographic, socioeconomic, behavior, and health information aboutindividual respondents, also contain, for example, biomarker informationassociated with lab tests such as the HbA1C level of the respondents.The set of respondents surveyed in the second dataset is not necessarilythe same individuals surveyed in the first dataset. The second datasetmay contain numeric attributes such as age or weight which can take anyvalue on a continuum. The second dataset may also contain categoricalattributes such as race which take on a finite number of values. Theindividuals surveyed may not answer one or more questions so each row ofthe second dataset may contain one or more missing values. The seconddataset may be, for example, an in person survey where it is difficultto reach many respondents and may be considered a small survey dataset(e.g., small scale survey data 152.)

Numeric attributes are binned (204). For example, the numeric attributesof the second dataset are converted to categorical attributes in thesame way as the first dataset. For those attributes that are the samebetween the first dataset and the second dataset, the same binningcutoffs are used.

Common attributes are matched (205). For example, the first dataset andthe second dataset may not be obtained by the same surveyor on the samedate. Therefore, common attributes between the first dataset and thesecond dataset are identified. Some attributes such as age arestraightforward to align because age is typically represented in allsurveys by years since birth. Other attributes such as activity levelmay be quantified as active or non-active in different ways. Based onthe way the survey questions are described, an expert can determine thebest way to label people as active or non-active in the two differentsurveys. Still other attributes may be collected with differentgranularity. For example, people of Chinese, Japanese, Korean, andIndian heritage may be classified as Asian in one survey while people ofthese different heritages may be classified separately in anothersurvey. One approach to match attributes in this case is to bin thefiner granularity survey into the coarser granularity so in both surveysthe individuals are classified as Asian.

Append dataset #1 to dataset #2 to create dataset #3 (206). For example,if the first dataset consists of 500,000 rows corresponding to 500,000individuals and the second dataset consists of 50,000 rows correspondingto 50,000 individuals, the third dataset will consist of 550,000 rowscorresponding to the 550,000 unique individuals surveyed. Each column ofdataset #3 will consist of questions asked either in the survey fordataset #1, the survey for dataset #2, or the question may be asked inboth surveys. If a question is asked in both datasets #1 and #2, theresponse in dataset #3 will exist for each of the 550,000 rows exceptfor nonresponses. If the question is asked in dataset #1 but not dataset#2, the response will exist for the first 500,000 rows but be missingfor the last 50,000 rows. If the question is asked in dataset #2 but notin dataset #1, then the response will be missing for the first 500,000rows.

After the data preparation step is complete, a one-hot encoded datasetmay be generated from the combined dataset #3. The one-hot encodeddataset is a dataset that specifies (e.g., with a value such as 1)wherever the response to a particular question was answered in theaffirmative for a particular category data exists, and with a value(e.g, with a value such as 0.) wherever the response to a particularquestion was answered in the negative for a particular category. Forexample, the single attribute such as age category young (18-40), middleaged (40-60), and old (60-100) will become three attributes: young age,middle age, and old age. A survey respondent who is 30 will have a 1 inthe young age attribute, 0 in the middle age attribute, and 0 in the oldage attribute. If the question was not answered by the respondent, orthe question was not present in the combined dataset, then the valuewill be missing for all attributes in the one-hot encoded dataset.

Batch-wise training is used to train the RBM. The process for trainingthe RBM is further detailed in FIG. 3. Generally, the process used bybatch-wise training is described as k-fold Contrastive Divergence.However, because of the missing values, at least one additional step isrequired to perform the usual k-fold Contrastive Divergence algorithm.

Dataset #3 is divided into batches (301) where a batch is a set of rowsin dataset #3. Dividing the data into a set of batches is done so thateach batch can be processed individually in sequence to train the RBM inthe k-fold Contrastive Divergence algorithm. A batch size may be, forexample, 64 rows.

RBM weights and biases are initialized (302). For example, the weightparameters and the node parameters of the RBM may be initialized.Initializing all the weight parameters of the RBM to one and the nodeparameters to zero is one possible choice. Each node, v, in the visiblelayer of the RBM may correspond to a unique value of each categoricalvariable in the attributes of dataset #3. The number of hidden nodes isan adjustable parameter of the RBM and determines how much thedimensionality of the data is reduced. During the training of the RBM, anode will take on a value of zero if the respondent's answer did notcorrespond to that category for the current row of the dataset and 1 ifthe respondent's answer did correspond to that category for the currentrow of the dataset. In an embodiment, the RBM has 128 hidden nodes. Eachedge connecting a visible node and a hidden node of the RBM ischaracterize by a weight parameter which is learned during the trainingof the RBM. In addition, each visible node and each hidden node ischaracterized by a parameter which will also be learned during trainingof the model.

A batch is selected and for each row (v) in the batch, the process inblocks 404-408 is performed (303). In other words, one of the batches ofthe training data from dataset #3 is used to incremental optimize (viablocks 304-308) the current state of the the RBM.

Gibbs sampling is performed (304). Some of the rows in the batch willhave attributes where the survey question was not responded to or wherethe survey question was not present. The values in the one-hot encodeddataset will be neither 0 or 1 but will be missing. For these rows, aninitial value will be determined from the initial conditions of thehidden notes and the visible nodes for which there is no missing value.In particular, missing data values for a row v are obtained by samplingthe current values of the hidden nodes according to the probabilitydistribution p(v_(missing)|v_(partial),h), where v_(partial) are thevisible nodes where data does exist, and h is the current values of thehidden nodes.

After creating estimates of the missing data in box 304, Gibbs samplingis performed alternatively between the visible layer and the hiddenlayer k number of times, where k is a selected parameter of thealgorithm. A counter t is set to zero (305). From the current values ofthe visible layer nodes, as well as the current parameters for theweights and the nodes, the next iteration of the hidden layer values arecalculated for each row in the batch according to the probabilitydistribution p(h_(i)|v^((t))) (306). Then from the current values of thehidden layer nodes as well as the current parameters for the weights andthe nodes, the next iteration of the visible layer values are calculatedfor each row in the batch according to the probability distributionp(v_(i)|^((t))) (307). If less than k iterations have been performed,flow proceeds to block 406 to perform another iteration. If the kiterations have been performed, flow proceeds to block 309.

The weight parameters and the node parameters are then incrementalupdated (309). This may be accomplished using the algorithm shown inTable 1. In Table 1, w_(ij) are the parameters associated with the edgesconnecting the m visible nodes and the n hidden nodes, b_(b) are theparameters associated with the m visible nodes, and ci are theparameters associated with the n hidden nodes. i and j index the visiblenodes and the hidden nodes, respectively.

TABLE 1 for  i = 1, …  , n, j = 1, …  , m  do$\left\lfloor \begin{matrix}\left. {\Delta w}_{ij}\leftarrow{{\Delta w}_{ij} + {{p\left( {H_{i} = \left. 1 \middle| \upsilon^{(0)} \right.} \right)} \cdot \upsilon_{j}^{(0)}} - {{p\left( {H_{i} = \left. 1 \middle| \upsilon^{(k)} \right.} \right)} \cdot \upsilon_{j}^{(k)}}} \right. \\\left. {\Delta \; b_{j}}\leftarrow{{\Delta \; b_{j}} + \upsilon_{j}^{(0)} - \upsilon_{j}^{(k)}} \right. \\\left. {\Delta \; c_{i}}\leftarrow{{\Delta \; c_{i}} + {p\left( {H_{i} = \left. 1 \middle| \upsilon^{(0)} \right.} \right)} - {p\left( {H_{i} = \left. 1 \middle| \upsilon^{(k)} \right.} \right)}} \right.\end{matrix} \right.$

After the RBM is trained, the RBM is used to impute values for missingvalues. In an embodiment, the imputed missing values may be from thedataset used to train the RBM (e.g., dataset #3). In another embodiment,the imputed missing values may be from a different dataset than was usedto train the model. In this instance, the different dataset may also beconcurrently used to update the RBM's model parameters.

FIG. 4 is a flowchart illustrating a method of imputing values formissing data. A row is selected from dataset #3 (401). For eachattribute that contains a missing value in the row, Gibbs sampling isperformed in order to assign an imputed value (402). In particular,missing data values for the selected row v are obtained by sampling thecurrent values of the hidden nodes according to the probabilitydistribution p(v_(missing)|v_(partial),h), where v_(partial) are thevisible nodes where data does exist, and h is the current values of thehidden nodes.

After creating estimates of the missing data in box 402, Gibbs samplingis performed alternatively between the visible layer and the hiddenlayer k number of times, where k is a selected parameter of thealgorithm. A counter t is set to zero (403). From the current values ofthe visible layer nodes, as well as the current parameters for theweights and the nodes, the next iteration of the hidden layer values arecalculated for each row in the batch according to the probabilitydistribution p(h_(i)|v^((t))) (404). Then from the current values of thehidden layer nodes as well as the current parameters for the weights andthe nodes, the next iteration of the visible layer values are calculatedfor each row in the batch according to the probability distributionp(v_(i)|v^((t))) (405). If less than k iterations have been performed,flow proceeds to block 404 to perform another iteration. If the kiterations have been performed, flow proceeds to block 407 (406). Theweights and node parameters of the trained RBM ensure that the imputedvalue is the highest likelihood value expected for the missing value.

If all of the rows in the dataset have had their missing values imputed,flow proceeds to block 408. If not all of the rows in the dataset havehad their missing values imputed, flow proceeds to block 401 to selectanother row. The imputed dataset is returned as an output (408).

The exemplary systems and methods described herein can be performedunder the control of a processing system executing computer-readablecodes embodied on a computer-readable recording medium or communicationsignals transmitted through a transitory medium. The computer-readablerecording medium is any data storage device that can store data readableby a processing system, and includes both volatile and nonvolatilemedia, removable and non-removable media, and contemplates mediareadable by a database, a computer, and various other network devices.

Examples of the computer-readable recording medium include, but are notlimited to, read-only memory (ROM), random-access memory (RAM), erasableelectrically programmable ROM (EEPROM), flash memory or other memorytechnology, holographic media or other optical disc storage, magneticstorage including magnetic tape and magnetic disk, and solid statestorage devices. The computer-readable recording medium can also bedistributed over network-coupled computer systems so that thecomputer-readable code is stored and executed in a distributed fashion.The communication signals transmitted through a transitory medium mayinclude, for example, modulated signals transmitted through wired orwireless transmission paths.

FIG. 5 illustrates an exemplary processing node 500 comprisingcommunication interface 502, user interface 504, and processing system506 in communication with communication interface 502 and user interface504. Processing node 500 is capable of paging a wireless device.Processing system 506 includes storage 508, which can comprise a diskdrive, flash drive, memory circuitry, or other memory device. Storage508 can store software 510 which is used in the operation of theprocessing node 500. Storage 508 may include a disk drive, flash drive,data storage circuitry, or some other memory apparatus. Software 510 mayinclude computer programs, firmware, or some other form ofmachine-readable instructions, including an operating system, utilities,drivers, network interfaces, applications, or some other type ofsoftware. Processing system 506 may include a microprocessor and othercircuitry to retrieve and execute software 510 from storage 508.Processing node 500 may further include other components such as a powermanagement unit, a control interface unit, etc., which are omitted forclarity. Communication interface 502 permits processing node 500 tocommunicate with other network elements. User interface 504 permits theconfiguration and control of the operation of processing node 500.

Implementations discussed herein include, but are not limited to, thefollowing examples:

Example 1: A method, comprising: training a neural network model tomodel a joint distribution of attributes across multiple health surveys,where the multiple health surveys include a first scale survey datasetsand a second scale survey datasets wherein the first scale surveydatasets have at least 10 times the number of entries as the secondscale survey datasets, the neural network model trained using a combineddataframe of the first scale survey datasets and the second scale surveydatasets that include missing value indicators; and using the jointdistribution of attributes modeled by the neural network model to imputesubstitute values for the missing value indicators to create an outputfirst scale dataset that does not include missing value indicators.

Example 2: The method of example 1, wherein the neural network model isa Restricted Boltzman machine which includes a visible layer comprisingvisible layer nodes and a hidden layer comprising hidden layer nodesthat are configured as a fully connected bipartite graph.

Example 3: The method of example 2, wherein training the neural networkmodel includes: estimating, based on current values of the hidden layernodes, first values for the visible layer nodes corresponding to themissing value indicators.

Example 4: The method of example 3, wherein the estimating first valuesfor the visible layer nodes corresponding to the missing valueindicators is based on sampling of the current values of the hiddennodes according to a first probability distribution function ofp(v_(miss)|v_(part),h), where v_(miss) are current values of the visiblelayer nodes corresponding to the missing value indicators, v_(part) arecurrent values of the visible layer nodes not corresponding to themissing value indicators, and h are the current values of the hiddennodes.

Example 5: The method of example 3, wherein training the neural networkmodel includes: alternately Gibbs sampling the visible layer and thehidden layer for k iterations, where k>1.

Example 6: The method of example 1, wherein imputing the substitutevalues for the missing value indicators includes: based on currentvalues of the hidden layer nodes obtained from the trained neuralnetwork model, second values for the visible layer nodes correspondingto the missing value indicators.

Example 7: The method of example 5, wherein the estimating second valuesis based on random sampling of the current values of the hidden nodesobtained from the trained neural network model according to a secondprobability distribution function of p(v_(miss), v_(part),h), wherev_(miss) are current values of the visible layer nodes corresponding tothe missing value indicators, v_(part) are current values of the visiblelayer nodes not corresponding to the missing value indicators, and h arethe current values of the hidden nodes.

Example 8: A method, comprising: receiving heterogenous survey datacomprising at least a first dataset having a first set of attributes anda second dataset having a second set of attributes, the first set ofattributes and the second set of attributes having at least one commonattribute and at least one attribute that is not in common between thefirst set of attributes and the second set of attributes, the firstdataset and the second dataset having at least one missing entry; and,training a Restricted Boltzmann Machine (RBM) having hidden nodes andvisible nodes using the first dataset and the second dataset, thetraining comprising: for a missing entry in at least one of the firstdataset and the second dataset, a value for the missing entry based on afirst randomly selected sample made according to a first jointprobability distribution of a value for the missing entry given a set ofcurrent visible node values and a set of current values for the hiddennodes.

Example 9: The method of example 9, further comprising: imputingsubstitute values for the at least one missing entry to create an outputdataset that does not include the at least one missing entry.

Example 10: The method of example 9, wherein the RBM is configured as afully connected bipartite graph.

Example 11: The method of example 10, wherein the first jointprobability distribution is p(v_(miss)|v_(part),h), where v_(miss) arecurrent values of the visible layer nodes corresponding to the at leastone missing entry, v_(part) are current values of the visible layernodes not corresponding to the at least one missing entry, and h are thecurrent values of the hidden nodes.

Example 12: The method of example 10, wherein training the RBM includes:alternately Gibbs sampling the visible layer and the hidden layer for kiterations, where k>1.

Example 13: The method of example 12, wherein imputing the substitutevalues for the at least one missing entry comprises: estimating, basedon current values of the hidden layer nodes obtained from the trainedRBM, second values for the visible layer nodes corresponding to the atleast one missing entry.

Example 14: The method of example 13, wherein the estimating secondvalues is based on sampling of the current values of the hidden nodesobtained from the trained neural network model according to a secondprobability distribution function of p(v_(miss)|v_(part),h), wherev_(miss) are current values of the visible layer nodes corresponding tothe at least one missing entry, v_(part) are current values of thevisible layer nodes not corresponding to the at least one missing entry,and h are the current values of the hidden nodes.

Example 15: A system, comprising: a neural network model operable tomodel a joint distribution of attributes across multiple health surveys,where the multiple health surveys include first scale survey datasetsand second scale survey datasets wherein the first scale survey datasetshave at least 10 times the number of entries as the second scale surveydatasets, the neural network model trained using a combined dataframe ofthe first scale survey datasets and the second scale survey datasetsthat include missing value indicators; and an imputation module to use ajoint distribution of attributes modeled by the neural network model toimpute substitute values for the missing value indicators to create anoutput first scale dataset that does not include missing valueindicators.

Example 16: The system of example 15, wherein the neural network modelincludes a visible layer comprising visible layer nodes and a hiddenlayer comprising hidden layer nodes that are configured as a fullyconnected bipartite graph.

Example 17: The system of example 16, wherein the neural network modeltraining included, based on current values of the hidden layer nodes,estimating first values for the visible layer nodes corresponding to themissing value indicators.

Example 18: The system of example 17, wherein the neural network modeltraining included estimating first values based on random sampling ofthe current values of the hidden nodes according to a probabilitydistribution function of p(v_(miss)|v_(part),h), where v_(miss) arecurrent values of the visible layer nodes corresponding to the missingvalue indicators, v_(part) are current values of the visible layer nodesnot corresponding to the missing value indicators, and h are the currentvalues of the hidden nodes.

Example 19: The system of example 17, wherein the neural network modeltraining included alternately Gibbs sampling the visible layer and thehidden layer for k iterations, where k>1.

Example 20: The system of example 15, wherein imputation of thesubstitute values for the missing value indicators included, based oncurrent values of the hidden layer nodes obtained from the trainedneural network model, estimating second values for the visible layernodes corresponding to the missing value indicators.

The above description and associated figures teach the best mode of theinvention. The following claims specify the scope of the invention. Notethat some aspects of the best mode may not fall within the scope of theinvention as specified by the claims. Those skilled in the art willappreciate that the features described above can be combined in variousways to form multiple variations of the invention. As a result, theinvention is not limited to the specific embodiments described above,but only by the following claims and their equivalents.

What is claimed is:
 1. A method, comprising: training a neural networkmodel to model a joint distribution of attributes across multiple healthsurveys, where the multiple health surveys include a first scale surveydatasets and a second scale survey datasets wherein the first scalesurvey datasets have at least 10 times the number of entries as thesecond scale survey datasets, the neural network model trained using acombined dataset of the first scale survey datasets and the second scalesurvey datasets that include missing value indicators; and using thejoint distribution of attributes modeled by the neural network model toimpute substitute values for the missing value indicators to create anoutput first scale dataset that does not include missing valueindicators.
 2. The method of claim 1, wherein the neural network modelis a Restricted Boltzman machine which includes a visible layercomprising visible layer nodes and a hidden layer comprising hiddenlayer nodes that are configured as a fully connected bipartite graph. 3.The method of claim 2, wherein training the neural network modelincludes: estimating, based on current values of the hidden layer nodes,first values for the visible layer nodes corresponding to the missingvalue indicators.
 4. The method of claim 3, wherein the estimating firstvalues for the visible layer nodes corresponding to the missing valueindicators is based on sampling of the current values of the hiddennodes according to a first probability distribution function ofp(v_(miss)|v_(part),h), where v_(miss) are current values of the visiblelayer nodes corresponding to the missing value indicators, v_(part) arecurrent values of the visible layer nodes not corresponding to themissing value indicators, and h are the current values of the hiddennodes.
 5. The method of claim 3, wherein training the neural networkmodel includes: alternately Gibbs sampling the visible layer and thehidden layer for k iterations, where k>1.
 6. The method of claim 1,wherein imputing the substitute values for the missing value indicatorsincludes: estimating, based on current values of the hidden layer nodesobtained from the trained neural network model, second values for thevisible layer nodes corresponding to the missing value indicators. 7.The method of claim 6, wherein the estimating second values is based onsampling of the current values of the hidden nodes obtained from thetrained neural network model according to a second probabilitydistribution function of p(v_(miss)|v_(part),h), where v_(miss) arecurrent values of the visible layer nodes corresponding to the missingvalue indicators, v_(part) are current values of the visible layer nodesnot corresponding to the missing value indicators, and h are the currentvalues of the hidden nodes.
 8. A method, comprising: receivingheterogenous survey data comprising at least a first dataset having afirst set of attributes and a second dataset having a second set ofattributes, the first set of attributes and the second set of attributeshaving at least one common attribute and at least one attribute that isnot in common between the first set of attributes and the second set ofattributes, the first dataset and the second dataset having at least onemissing entry; and training a Restricted Boltzmann Machine (RBM) havinghidden nodes and visible nodes using the first dataset and the seconddataset, the training comprising: estimating, for a missing entry in atleast one of the first dataset and the second dataset, a value for themissing entry based on a first randomly selected sample made accordingto a first joint probability distribution of a value for the missingentry given a set of current visible node values and a set of currentvalues for the hidden nodes.
 9. The method of claim 8, furthercomprising: imputing substitute values for the at least one missingentry to create an output dataset that does not include the at least onemissing entry.
 10. The method of claim 8, wherein the RBM is configuredas a fully connected bipartite graph.
 11. The method of claim 10,wherein the first joint probability distribution isp(v_(miss)|v_(part),h), where v_(miss) are current values of the visiblelayer nodes corresponding to the at least one missing entry, v_(part)are current values of the visible layer nodes not corresponding to theat least one missing entry, and h are the current values of the hiddennodes.
 12. The method of claim 10, wherein training the RBM includes:alternately Gibbs sampling the visible layer and the hidden layer for kiterations, where k>1.
 13. The method of claim 12, wherein imputing thesubstitute values for the at least one missing entry comprises:estimating, based on current values of the hidden layer nodes obtainedfrom the trained RBM, second values for the visible layer nodescorresponding to the at least one missing entry.
 14. The method of claim13, wherein the estimating second values is based on random sampling ofthe current values of the hidden nodes obtained from the trained neuralnetwork model according to a second probability distribution function ofp(v_(miss)|v_(part),h), where v_(miss) are current values of the visiblelayer nodes corresponding to the at least one missing entry, v_(part)are current values of the visible layer nodes not corresponding to theat least one missing entry, and h are the current values of the hiddennodes.
 15. A system, comprising: a neural network model operable tomodel a joint distribution of attributes across multiple health surveys,where the multiple health surveys include first scale survey datasetsand second scale survey datasets wherein the first scale survey datasetshave at least 10 times the number of entries as the second scale surveydatasets, the neural network model trained using a combined dataset ofthe first scale survey datasets and the second scale survey datasetsthat include missing value indicators; and an imputation module to use ajoint distribution of attributes modeled by the neural network model toimpute substitute values for the missing value indicators to create anoutput first scale dataset that does not include missing valueindicators.
 16. The system of claim 15, wherein the neural network modelincludes a visible layer comprising visible layer nodes and a hiddenlayer comprising hidden layer nodes that are configured as a fullyconnected bipartite graph.
 17. The system of claim 16, wherein theneural network model training included, based on current values of thehidden layer nodes, estimating first values for the visible layer nodescorresponding to the missing value indicators.
 18. The system of claim17, wherein the neural network model training included estimating firstvalues based on random sampling of the current values of the hiddennodes according to a probability distribution function ofp(v_(miss)|v_(part),h), where v_(miss) are current values of the visiblelayer nodes corresponding to the missing value indicators, v_(part) arecurrent values of the visible layer nodes not corresponding to themissing value indicators, and h are the current values of the hiddennodes.
 19. The system of claim 17, wherein the neural network modeltraining included alternately Gibbs sampling the visible layer and thehidden layer for k iterations, where k>1.
 20. The system of claim 15,wherein imputation of the substitute values for the missing valueindicators included, based on current values of the hidden layer nodesobtained from the trained neural network model, estimating second valuesfor the visible layer nodes corresponding to the missing valueindicators.